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This article is part of the supplement: IUFRO Tree Biotechnology Conference 2011: From Genomes to Integration and Delivery

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In search for the role of thermospermine synthase gene in poplar vascular development

Ana Milhinhos1*, Andreia Matos1, Francisco Vera-Sirera2, Miguel Blazquez2 and Célia Miguel1

Author Affiliations

1 Instituto de Tecnologia Química e Biológica-Univ. Nova de Lisboa; Instituto de Biologia Experimental e Tecnológica (ITQB-UNL;IBET) Av. República, EAN, 2780-157 Oeiras, Portugal

2 Instituto de Biología Molecular y Celular de Plantas (CSIC-UPV) 46022 Valencia, Spain

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BMC Proceedings 2011, 5(Suppl 7):P72  doi:10.1186/1753-6561-5-S7-P72

The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1753-6561/5/S7/P72


Published:13 September 2011

© 2011 Milhinhos et al; licensee BioMed Central Ltd.

This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background

Plant polyamines are preferentially detected in actively growing tissues and have been implicated in growth and developmental processes such as embryogenesis, floral developmental, fruit ripening, senescence and stress responses [1]. Recently it has been established a link between polyamines and vascular development as it was found that, in Arabidopsis, the loss-of-function mutants of ACAULIS5 (ACL5) gene, encoding thermospermine synthase, exhibit a severe dwarf phenotype, suggesting that thermospermine acts as a regulator of stem elongation [2,3]. However, in trees, no studies have yet been reported. Due to the relevance of vascular development in wood formation we are investigating the role of thermospermine in vascular tissues of poplar.

Materials and methods

A search for ACL5-like sequences in Populus trichocarpa genome allowed us to identify three putative ACL5 orthologous genes. Based on the degree of sequence similarity, we have selected one of them, PtACL5, to generate transgenic plants bearing the constructs for overexpression and silencing of this gene in poplar.

Results

High expression levels of PtACL5 in overexpression transgenic lines have been found to be correlated to higher thermospermine content in leaves and young stems, but not to a higher level of other polyamines, suggesting that PtACL5 encodes a thermospermine synthase in poplar, and it is most probably an ortholog of ACL5 in poplar. Interestingly, these plants display altered and arrested shoot development in the early stages following p35S::PtACL5 transformation, as well as severe dwarfism. Anatomical changes associated to the lack of elongation include arrested development of the root system and no elongation of the stem from the first internode onwards. Because Arabidopsisacl5 loss-of-function mutants show accelerated vessel cell death and ACL5 expression is confined to xylem vessel elements [4], we further looked for alterations in the vascular pattern of the poplar stem, and observed the development of a wider stem in dwarf plants, composed of primary vascular tissues only, lower number of metaxylem cells and with no secondary growth.

Conclusions

Overall, our results suggest that thermospermine has a regulatory role in xylem differentiation/maturation in poplar. Although a feedback control of thermospermine synthesis seems to be present in Arabidopsis, in our transgenic poplar the high levels resulting from overexpression of thermospermine synthase gene seem to overcome any turn-over that might be occurring of the excess thermospermine being produced. Currently we are pursuing the spatial localization of the ACL5 transcript in poplar plants through in situ hybridization, and by taking advantage of the generated transgenic lines we hope to understand the role of thermospermine in the vascular tissues formation in this woody species.

Acknowledgements

This work is supported by the FCT project PTDC/AGR-GPL/098369/2008 and FCT PhD grant SFRH/BD/30074/2006 (A.M.). Dr. Max Cheng for providing P.trichocarpa Nisqually-1 clone and Dr. Brian Jones for T89 hybrid clone.

References

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    Trends Plant Sci 1997, 2:124-130. Publisher Full Text OpenURL

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